The present invention relates to a process for the control of a brake unit for automotive vehicles in which process an electrical brake system is used. Electric signals which are generated dependent on the operation of the brake pedal, are processed electronically and are logically linked to signals derived from the brake power, the braking effect and/or the rotational behavior of the wheels. The electrically actuatable wheel brakes are controlled by means of these signals.
Electrical brakes for automotive vehicles are known in which by means of the brake pedal an ohmic resistance is varied which determines the energy flow to an electromagnet that exerts a brake pressure on the pertaining wheel brake corresponding to the power brought to bearing on its armature (German patent specification No. 851,602). A hand lever may interfere in the lever mechanism which transmits the force from the magnet to the friction lining of the wheel brake and, consequently, a brake pressure independent of the field of strength of the magnet may be transmitted mechanically to the wheel brake.
Furthermore, an electrical brake system is known in which an electric motor acts through a spindle on a piston which is, on its part, connected hydraulically with the piston of a wheel brake. In this configuration, the control signal to actuate the motor and, therefore, to apply and release the wheel brake is determined by the bridge voltage of a Wheatstone bridge which is furnished with two variable resistances, one of which being adjusted proportionally to the operation of the brake pedal. The setting of the second variable resistance is dependent on the hydraulic brake pressure. In addition, a logic intervenes in the bridge circuit, which logic receives output signals from a sensor monitoring the rotational behavior of the wheels (German patent application No. 2,128,169). The brake fails in the event of a failure of the electric power supply or in the event of an electric component becoming defective.
In a further known electrical vehicle brake unit (German patent application No. 2,926,017), the operation of the brake pedal leads to the generation of a digital signal being redundantly transmitted through two sensors to a control logic which furnishes output signals for an electric motor dependent on different sensor signals. The electric motor generates brake pressure for a hydraulic wheel brake through a spindle and the piston of a pressure modulator. Thus unit also requires an emergency brake which renders it possible to brake the vehicle in case of a failure of the source of the electrical energy or of a fault in the electrical system.
The object of the present invention is to overcome the inconveniences of the known electrical brake systems and to create a process for the control of an electronically controllable and adjustable heavy-duty brake unit which allows to be realized in the shape of a comparatively simple brake unit requiring but little effort for its manufacture and which renders it possible to safely brake the vehicle even in the event of a failure or a fault of the electric power supply or of the electric components.